Wireless local area networks (WLANs) are gaining in popularity, and new applications are being developed. The original WLAN standards, such as “Bluetooth” and IEEE 802.11, were designed to enable communications at 1-2 Mbps in a band around 2.4 GHz. More recently, IEEE working groups have defined the 802.11a and 802.11b extensions to the original standard, in order to enable higher data rates. The 802.11a standard envisions data rates over 20 Mbps over short distances in a 5 GHz band, while 802.11b defines data rates up to 11 Mbps in the 2.4 GHz band. For 11 Mbps operation, the 802.11b standard uses complementary code keying (CCK) or quadrature phase shift keying (QPSK) with packet binary convolutional coding (PBCC). These modulation schemes are further described in tho IEEE 802.11b standard, which is incorporated herein by reference.
Recently the IEEE 802.11 working group has called for proposals to extend the 802.11b standard data rates still further, to 22 Mbps and above. One proposal that has been put forth, by Kodak and Motorola, is based on a wideband binary frequency shift keying (BFSK) scheme, with a bandwidth of up to 28 MHz. While this proposal in itself can be implemented in a straightforward way, using analog signal processing, it is not compatible with existing, lower-rate receivers or with Bluetooth protocols. Furthermore, it will typically enable high data-rate communication only over very short distances, on the order of 2 m.
Convolutional coding, as mentioned above, is widely used in communication applications to reduce the bit error rate (BER) in signals sent over noisy channels. Pragmatic trellis coded modulation (PTCM) is a particularly useful type of convolutional coding, which has the advantages of reduced computation load and efficient implementation in VLSI devices. PTCM encoders and decoders are capable of handling different modulation techniques, such as binary phase shift keying (BPSK), QPSK, 8-PSK and 16-PSK (referred to collectively as M-PSK techniques). An exemplary trellis encoder and decoder based on PTCM are described in U.S. Pat. No. 5,633,861, whose disclosure is incorporated herein by reference.